Coatings on colloidal nanoparticles can help stabilize particles to enhance their unique optical, catalytic and magnetic properties [1]. Colloidal stabilization is commonly attained via deposition of a homogeneous silica coating by core-shell nanotechnology [2]. Silica has been preferred as the coating material as it has several advantages over other organic or inorganic coating materials, such as chemical inertness, optical transparency and the ability to produce concentrated dispersions of nanosized materials by preventing coagulation during chemical reactions. Depending on chemical affinity, certain metal particles can be directly coated with silica. However, many materials lack this affinity, and in these cases, the materials can be coated with surface functionalizers, which simultaneously act as silane coupling agents. In the literature, nanocoating of colloidal nanoparticles has included: metals (Au, Ag, Fe/Fe2O3), semiconductors (CdS, ZnS, CdSe/ZnSe), polymers (polysterene, PDMS), and inorganic oxides (boehmite rods, gibbsite platelets). However, silica coated copper nanoparticles are absent. In this study, Cu colloidal nanoparticles, ranging in size from 25-125nm (Mesocopper: Purestcolloid Inc.) were coated with a SiO2 nanolayer. Polyvinylpyrrolidone (PVP) and sodium dodecyl benzene sulphonate (SDBS) were used as the surfactants (and simultaneously as surface functionalization linkers) to stabilize the core nanoparticles as well as to facilitate adherence of SiO2 on the particle surface. Tetraethoxysilane (TEOS) was used as the shell building material to synthesize the silica nanolayer. Aqueous ammonia and ethanol were used as the catalyst and the solvent respectively. The resulting core-shell nanostructures were characterized by TEM, SEM, and FTIR. Fourier Transform Infrared Spectroscopy was used to identify chemical groups at each stage of the coating process. UV-visible spectroscopy was used to observe changes in optical properties of the coated nanoparticles, and transmission electron microscope (TEM) as well as scanning electron microscope (SEM) were used to assess average particle diameter, silica shell thickness, and overall morphology of the core-shell nanostructures. TEM was more advantageous than SEM because it allowed the metal core particles to be observed along with the silica layer. The effects of different parameters, such as, concentration of silane (TEOS), concentration of stabilizer (PVP/SDBS) and time of aging, on the growth morphology of the silica nanoshells were compiled.

Supported by the grants from Department of Energy (DOE) Sustainable Energy Research Center (SERC) at MSU.

1. Z. Zhang, R.C. Patel, R. Kothari, C.P. Johnson, S.E. Friberg, P.A. Aikens (2000) J. Phys.Chem. B 104: 1176. 2. L.M. Liz-Marzán, M. Giersig, P.Mulvaney (1996) Langmuir 12: 4329.